The present invention relates to a method of detecting accumulations of particles, for instance metaphase plates, as the same may be caused to be viewable in a microscope image, wherein the image is converted by a raster process into raster elements which are electronically scanned, treated, and evaluated, using decision logic to determine whether each individual raster element fits or does not fit the criteria for which an evaluation is sought.
In order to measure the size, shape and number of desired particles or other features of a flat image of the character indicated, this image is scanned in raster-form by a beam of light or electrons. Electric signals are thereby produced in a receiver such as a photocell, a photomultiplier or a television camera. These scanning signals are fed for evaluation to a so-called discriminator which produces binary signals, of time duration corresponding to line-scanned chord length in the objects to be evaluated.
For better digital evaluation, a generator is used to produce a high frequency voltage, and this generator is synchronized with movement of the scanning beam (U.S. Pat. No. 2,494,941, West German Provisional Patent AS 1,423,636). This generator supplies a voltage which divides the image or the scan lines into individual raster elements.
For further processing of the digitalized image which has been divided into raster elements, various methods are known, under the name "texture analysis".
German Pat. No. 2,128,690 describes a device for the texture analysis of a non-homogeneous object. The device contains logical-analysis and counter circuitry to recognize and count such objects. This device contains a circuit arrangement by means of which it is decided whether an image-structure element fits predetermined criteria for the object under examination; to this end, delay-storage devices and comparators are used. The storage devices delay incoming image signals for periods of time which correspond on the one hand to the distance between two raster elements of one line each, and which correspond on the other hand approximately to a line length. In the comparators, actual values of image signals which lie alongside of each other in different directions are compared with each other, to thereby give information concerning the entire content of the structure element. Upon the evaluation, the structure element is displayed stepwise along the scanning lines in the image examined, an output signal being produced, for instance, when the structure element is located completely within an image particle.
U.S. Pat. No. 3,967,053 describes an arrangement in which each raster element has an associated preset digital value which, within the limits of each object to be evaluated, is decremented one bit at a time in at least one pre-selected direction in successive scanning lines until a pre-selected guide or criteria value is reached. The only image signals which pass for further evaluation are those for which a raster element has an associated preset signal value which accords with the guide value. By selective connection of delay members, delay time is established to determine the displacement of raster elements in successive lines and thus the direction of length discrimination.
Devices of the character indicated have long been used for automatic evaluation of the most varied structures and are useful in many fields of application. However, they are not sufficiently efficient for detection of very complex structures. Thus, for example, for automatic detection of metaphase plates, the recent trend has been to use methods in which digitalized image signals are fed immediately to a computer for further processing. While it is true that almost any complex program can be processed in a computer, the fact remains that, even with relatively simple programs, computer-processing times become too great, unless one uses an extremely large computer system which is too expensive for routine instruments. In searching for metaphase plates, traditional computers or microprocessor circuits are either too expensive or are not sufficiently efficient, so that the sampling of preparations is too time-consuming.
Metaphase plates are accumulations of chromosomes (of a cell) which accumulations are the product of a special technique by which they have been separated from other components of the cell. In good metaphase plates, the chromosomes are distributed over a surface which is considerably larger than one cell. In poor metaphase plates, the chromosomes "stick" to each other and cover a surface which is only slightly larger than one cell.
In biology and medicine, the automatic detection of metaphase plates is gaining increasing importance. Practical uses are the detection of genetic damage in early pregnancy (amniocentesis) and successive investigations of radiation damage. In the latter case particularly, it is necessary to evaluate a very large number of metaphase plates, which must previously be found on a slide beneath a microscope. There are practical applications in which more than 99% of the surface on a slide contains uninteresting cells and impurities; less than 1% of the surface, typically 0.1% of the surface, has metaphase plates suitable for evaluation.